Research: In recent years, intensive effort has focused on the investigation of biological approaches for the treatment of cancer, including immunotherapy utilizing cytokines, antibodies and/or vaccines, gene therapy as well as inhibition of tumor angiogenesis among others. Although immunotherapeutic approaches such as systemic administration of interleukin-2 (IL-2) have provided meaningful benefit to some patients with metastatic renal cell carcinoma or melanoma, many questions remain regarding the best approach to maximize the potential efficacy of biological therapy. Given the complexity of signals engaged during the host antitumor immune response, and the intricate network of interactions within the tumor microenvironment, it appears that much as occurred with the clinical evolution of combination chemotherapy, the full potential of biological therapies for cancer will most likely be realized using rationally-designed combinations of agents with complementary mechanisms of action.[unreadable] [unreadable] Laboratory studies: We investigate molecular mechanisms by which the host immune response may be engaged to induce alterations in the tumor microenvironment to effect disease regression (i.e. modulation of tumor neovascularization, induction of tumor and/or endothelial apoptosis, etc.), and also use these observations to facilitate the design of novel biologically-targeted treatment strategies for neuroblastoma and/or renal cell carcinoma. Much of our recent effort has focused on investigation of the antitumor activity of two cytokine-based combinations, IL-12/pulse IL-2 and IL-18/IL-2, and delineation of the respective mechanisms which mediate their therapeutic efficacy. In mice bearing well-established primary and/or metastatic neuroblastoma or renal cell carcinoma tumors, systemic administration of IL-12/pulse IL-2 can induce complete durable tumor regression in 80% or more of treated mice. Comparable responses are achieved after treatment with IL-18+/- IL-2. These studies have now defined several of the critical mechanisms by which these therapies can modulate the local tumor microenvironment to induce disease regression. Notably, IL-12/pulse IL-2 induces rapid vascular endothelial injury with tumor and/or endothelial apoptosis, inhibits tumor neovascularization and mediates CD8+ T cell-dependent tumor regression via mechanisms which share a common dependency on IFN-gamma and the Fas/Fas-L apoptosis pathway. Collectively, these observations suggest a mechanism whereby CD8+ FAS-L+ T cells may infiltrate the local tumor site and interact with Fas+ vascular endothelial and/or tumor cell populations to induce apoptosis, inhibition of angiogenesis, and ultimately, overall tumor regression. In mice bearing neuroblastoma tumors, IL-12 not only upregulates proapoptotic pathways within the tumor cell compartment, but also downregulates prosurvival factors (AKT) that may otherwise confer an intrinsic resistance to apoptosis. Similar but distinct mechanisms may be engaged by combined administration of IL-18/IL-2. More recent studies from our laboratory have now investigated the antitumor activity and mechanisms of action by IL-12 related cytokines including IL-23 and IL-27, and have demonstrated that these cytokines mediate potent antitumor effects in preclinical models of murine neuroblastoma and renal cell carcinoma. Our studies suggest that these cytokines may engage novel antitumor mechanisms and be rationally combined with existing antitumor cytokines such as IL-2 and/or IL-12 as well to achieve an improved spectrum of therapeutic efficacy. In other studies, we are investigating mechanisms by which inhibitors of proteasome function can potentiate the proapoptotic and overall antitumor activity of cytokines such as IL-2 and IL-12.